The closest thing to a clue in the search for a missing commercial jetliner are oil slicks in the Gulf of Thailand where all contact was lost with the flight, which was en route from Kuala Lumpur to Beijing.

A Vietnamese search plane, part of a massive, multinational search effort, spotted the oil slicks that stretch between 6 and 9 miles, the Vietnam government's official news agency reported. The traces of oil were found about 90 miles south of Tho Chu Island, the report said, in the same area where the flight disappeared from radar early Saturday morning.

The oil discovery only added to a growing list of questions about the fate of the plane carrying 227 passengers and 12 crew members: When and where did the plane go, and who exactly was on board?

"It has been more than 24 hours since we last heard from MH370. ...The search and rescue team is yet to determine the whereabouts of the Boeing 777-200 aircraft," the airline said in a statement posted to its website. At this stage, search and rescue efforts "have failed to find evidence of any wreckage."

In the meantime, the search area in the South China Sea is being expanded and efforts to locate the plane will continue overnight and into early Sunday morning, said Azharuddin Abdul Rahman, director general of civil aviation in Malaysia.

Passenger manifest questioned

Bits and pieces of information have begun to form, but it remains unclear how they fit into the bigger picture, if at all.

For instance, after the airline released a manifest, Austria denied that one of its citizens was aboard the flight. The Austrian citizen was safe and sound, and his passport had been stolen two years ago, Austrian Foreign Ministry spokesman Martin Weiss told CNN.

Similarly, Italy's foreign ministry confirmed that no Italians were on MH370, even though an Italian was listed on the manifest. Police in Italy said the man's passport was stolen last year.

A U.S. intelligence official said authorities are aware of reporting about lost or stolen passports used by passengers on the missing flight.

"No nexus to terrorism yet," the official said, "although that's by no means definitive. We're still tracking."

Malaysian authorities reiterated during a news conference that they are not ruling anything out regarding the missing aircraft.

China, Vietnam, Singapore and Malaysia were conducting search and rescue operations south of Tho Chu island in the South China Sea, according to the airline and reports from Xinhua, China's official news agency. Ships, helicopters and airplanes are being utilized.

The USS Pinckney, a destroyer conducting training in the South China Sea, is being routed to the southern Vietnamese coast to aid in the search, the U.S. Navy said. The United States is also sending a P-3C Orion surveillance plane from Japan to provide long-range search, radar and communications capabilities, the Navy said.

Meanwhile, the Chinese Coast Guard has ordered on-duty vessels to aid in the search, Xinhua reported, citing government officials. China also sent a diving and salvage team to the area where the airplane is suspected to have gone down, as well as a Coast Guard vessel, the news agency reported.

Even so, officials appeared resigned to accepting the worst outcome.

"I'd just like to say our thoughts and prayers are with the bereaved families," Malaysian Prime Minister Najib Razak said during a news conference.

Grief, especially in China

More than half the passengers were Chinese.

Relatives of the 154 Chinese citizens on board gathered Saturday at a hotel complex in the Lido district of Beijing as a large crowd of reporters gathered outside.

"My son was only 40 years old," one woman wailed as she was led inside. "My son, my son. What am I going to do?"

Family members were kept in a hotel conference room, where media outlets had no access. Most of the familymembers have so far refused to talk to reporters. The airline said the public can call +603 7884 1234 for further information.

The Boeing 777-200 ER departed Kuala Lumpur International Airport at 12:41 a.m. and was expected to land in Beijing at 6:30 a.m., a 2,300-mile (3,700 kilometer) trip. It never arrived.

The plane carried 227 passengers, including five children under 5 years old, and 12 crew members, the airline said. Air traffic control in Subang, in Malaysia, had last contact with the plane.

At the time of its disappearance, the Malaysia Airlines plane was carrying about 7.5 hours of fuel, an airline official said.

Among the passengers there were 154 people from China or Taiwan; 38 Malaysians, and three U.S. citizens.

The airline's website said the flight was piloted by a veteran.

Capt. Zaharie Ahmad Shah, a 53-year-old Malaysian,

has 18,365 total flying hours and joined Malaysia Airlines in 1981, the website said. The first officer is Fariq Ab Hamid, 27, a Malaysian with a total of 2,763 flying hours. He joined Malaysia Airlines in 2007.

Still an 'urgent need' to find plane

"The lack of communications suggests to me that something most unfortunate has happened," said Mary Schiavo, former inspector general of the U.S. Department of Transportation, in an interview with CNN International.

"But that, of course, does not mean that there are not many persons that need to be rescued and secured. There's still a very urgent need to find that plane and to render aid," she said.

Malaysia Airlines operates in Southeast Asia, East Asia, South Asia, the Middle East and on the route between Europe and Australasia.

It has 15 Boeing 777-200 ER planes in its fleet, CNN's Richard Quest reported. The missing airplane was delivered to Malaysia Airlines in 2002.

Part of the company is in the private sector, but the government owns most of it.

Malayan Airways Limited began flying in 1937 as an air service between Penang and Singapore. A decade later, it began flying commercially as the national airline.

In 1963, when Malaysia was formed, the airline was renamed Malaysian Airlines Limited.

Within 20 years, it had grown from a single aircraft operator into a company with 2,400 employees and a fleet operator.

If this aircraft has crashed with a total loss, it would the deadliest aviation incident since November 2001, when an American Airlines Airbus A300 crashed in Belle Harbor, Queens, shortly after takeoff from JFK Airport. Killed were 265 people, including five people on the ground.